How really worth are the African endogenous knowledge and know-how? Why and how can we promote this inheritage, while the so-called western scientific model looks like the best means of knowing and mastering the world? This book answers these questions by examining ifa, a West-African system of knowledge and practices which a narrow knowledge reduces to a fanciful divinatory art, an art then logically "perceived as inconsistent and theoretically useless". Yet, more than a divinatory art, ifa, when we submit it to analysis, appears to be an organized set of knowledge and researches, a science in the making. What makes us really think that way is the intellectual vocation that defines ifa, the rigor of the logical operations that it implies and which recalls in one way or the other the game of implicit mathematics, the objectivity requirement which is valued by the actors of the system and rests on a genuine critical tradition. This opinion is also based on the weight of myths upon which ifa rests and which constitute an important granary where a prominent set of knowledge is packed. Beyond the establishment of the consistency and the limitations of ifa, this book has strived to define a "method" of examination and validation of the knowledge which has emerged out of the official scientific system. In fact, the questions which arise from it are finally intended to give a new foundation to philosophy of sciences and to epistemology.